Watershed characteristics

2.1.1 Geographical and morphological characteristics

The Valmasino watershed (Fig. 1) is located in the Central Alps at the border between Italy and Switzerland and it is situated between latitudes 46°09' N and 46°17' N and longitudes 9°34' E and 9°45' E.

The upstream drainage area measures 188 km2 with important glaciers located in the upper part. Its physiographical characteristics are formed by four valleys with the main Masino river flowing from north to south and four lower order valley elongated E-W. The Valmasino watershed represents a typical Alpine morphology characterised by great relief energy, high variability of steep slopes, variable aspects and cast shadows. Elevation ranges between 265 m a.s.l. (Ardenno village) and 3678 m a.s.l. at the summit of the Monte Disgrazia peak. As shown in Table 1, more than 90% of the entire catchment surface is located above 1000 meters and more than 70% of surfaces have a slope greater than 25°.

Table I. Morphometries! characteristies of the Valmasino watershed

Altitude (m a.s.l.)

Area (%)

265-1000

8

1000-2000

36

2000-3000

53

>3000

Slope j

Area I

24 31 40

Aspect H

Area {%)

315-45

17

45-135

24

135-225

35

225-315

24

Figure 1. The Valmasino catchment experiment site located in the Central Italian Alps

2.1.2 Climatological and hydrological characteristics

The meteorological station of Sondrio located at 298 m a.s.l. collected the most important time series data set, beginning in 1958 (ERSAL, 1992). The mean annual air temperature is 11 °C. The isothermal trend describes the role of the slope exposure, with the eastern slopes colder and the related agriculture activities taking place at lower elevations. The vertical thermal gradient is strongly affected by inversion phenomena. Annual potential evapotranspiration is 696 mm. Mean annual rainfall is 948 mm with the rainy season in summer (maximum monthly rainfall depth: 106 mm, in August) and a dry season during winter, with a long period of scarce rainfall (minimum monthly rainfall depth: 39 mm, in February). Extreme events can be considered to occur when more than 100 mm of rain falls in 24 hours. The hydrological regime of the Masino river is typically Alpine, showing maximum water flow during the late spring-early summer and minimum flow during the winter season.

2.1.3 Land cover and vegetation characteristics

The Valmasino catchment is sparesely urbanised and the dominant land use is devoted to pasture. The alluvial plain is dedicated to agricultural activities, mainly maize and staple meadows. Slopes and high areas are covered by spontaneous vegetation. Forested areas, including deciduous and evergreen forests, cover about 30%, in the remnant areas rock outcrops and debris are dominant.

Vegetation in the study area can be schematised in three zones changing with altitude (Giacomini, 1960). The lower part of the catchment includes the mountainous zone, characterised by fully covered evergreen, deciduous and mixed forests with main tree species represented by Fagus sylvatica, Picea abies and Larix decidua. The sub-Alpine zone is characterised by open woodland and shrubs, with the main trees species of Pinus mugo, Pinus cembra and Larix decidua. Brushes and tundra mainly constitute the vegetation cover of the Alpine zone (above 2000 m), with dominance of Rhododendron.

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